In the related art, various countermeasures have been taken for noise in radio communication between a vehicle and a portable device (FOB) for operating the vehicle. For example, Japanese Unexamined Patent Application Publication No. 2004-197649 discloses an engine control system that can guarantee communication with high reliability in which deterioration due to noise is prevented. In the engine control system, interactive communication is performed between a portable device on a user side and a transceiver on a vehicle side, a motor having a high-voltage battery as a power source is provided, and the operation of a switching noise source connected to the battery is limited when communication is performed between the portable device and the transceiver.
Japanese Unexamined Patent Application Publication No. 2007-191891 discloses a remote control system for an onboard device that can improve reliability of radio communication with a portable device without deteriorating convenience. The remote control system for an onboard device includes an onboard device and a portable device, and the portable device includes a received magnetic field intensity detecting unit that detects a reception state from the onboard device and returns RSSI information which is information indicating the reception state detected by the received magnetic field intensity detecting unit when receiving a call signal transmitted from the onboard device. The onboard device displays the received RSSI information with an alarm unit and allows a user to check that the system can normally operate even at the time of activation of the onboard device in which electromagnetic noise of the vehicle interfering with the radio communication with the portable device increases.
Japanese Unexamined Patent Application Publication No. 2003-191824 discloses a remote control system for an onboard device that can guarantee a stable communication area before starting a vehicle power source and suppress an occurrence of a communication error due to driving thereof after starting the vehicle power source in regard to communication between the onboard device and a portable device. The remote control system for an onboard device is provided with an onboard device that can transmit request signals having different frequencies and a portable device that can receive the request signals having different frequencies, which have been transmitted from the onboard device. When engine starting control is performed before starting an engine, downlink communication from the onboard device to the portable device is performed using radio waves of a low frequency of 134 kHz. On the other hand, when a process of checking whether the portable device is present in the vehicle interior is performed after starting the engine, the downlink communication from the onboard device to the portable device is performed using radio waves of a high frequency of 300 MHz.
Japanese Unexamined Patent Application Publication No. 2006-103355 discloses a smart keyless control system that can avoid an influence of electromagnetic noise from onboard electrical devices and rapidly restart an engine. The smart keyless control system determines whether an engine starting operation is performed within a predetermined amount of time from the previous engine stop when the engine starting operation satisfies a predetermined condition. The engine start is permitted through in-vehicle authentication when the engine starting operation is performed within the predetermined amount of time from the previous engine stop, and the engine start is permitted without the authentication when the engine starting operation is performed after the predetermined amount of time elapses from the previous engine stop. When the engine start is permitted without the authentication, a response request signal is transmitted with a high transmission intensity for the authentication after the predetermined amount of time elapses.
Japanese Unexamined Patent Application Publication No. 2010-223052 discloses an onboard device that can satisfactorily transmit a control result of a vehicle to a portable device with low power consumption. The onboard device detects an intensity of a signal when the signal is received from the portable device, and returns a signal indicating a vehicle control process of controlling the vehicle and a control result thereof to the portable device with an intensity corresponding to the detected intensity of the signal in response to the received signal.
Japanese Unexamined Patent Application Publication No. 2006-089946 discloses a portable device that can easily and satisfactorily control a communication-enabled area with a controller. The portable device performs interactive radio communication with an onboard device for controlling a door lock driving device or an engine starting device of a vehicle and remotely controls the onboard device on the basis of the communication. The portable device receives a request signal transmitted from the onboard device and decreases or increases the reception sensitivity thereof by a predetermined sensitivity level to adjust the reception sensitivity.
Japanese Unexamined Patent Application Publication No. 2010-265611 discloses a remote control system that can simply set a communication area corresponding to a remote control target. The remote control system wirelessly transmits information on the response sensitivity of a portable device suitable for a vehicle (vehicle type or the like) when a registration request signal for requesting for performing a portable device registering process is input from the outside. When information on the response sensitivity wirelessly transmitted from the vehicle side is received, the portable device sets its response sensitivity on the basis of the information and wirelessly transmits its specific identification information to the vehicle side.